With the hydrocarbon fuels prices going up and the renewable fuel mandate and the environmental advantages of the biodiesel as mentioned above it is expected that there will be activity in this area so as to supplement the hydrocarbon fuels, which will help in reducing demand of Crude oil.
The process is based on esterification of five fatty acid, a pretreatment step so as to enhance the yield of methyl esters in transesterification reaction. The esterification reaction is done with free fatty acids in Feed with methanol in the presence of a cation acid ion exchange resin catalyst Lewatit K 2621, K 2620 or equivalent (Rohm Haas Amberlyst 15 or 35 or Dowex M 31) at a WHSV of 2 to 5. This removes most of Free Fatty acids and increases the yield of Biodiesel. The reaction conditions are in 100 to 200 F temperature and pressure of 20 to 150 psig (preferably 50 psig and temperature of 140 F) to perform this reaction in the Esterification reactor.
The second reaction to is transesterification of triglycerides from oil or fats with methanol in the presence of alkaline catalyst. The catalysts that are being used are in homogeneous form, predominantly KOH. New processes have started using hetrogeneous catalyst that improves the process in removing major liquid wastes from this process, which are due to homogeneous catalyst use. RHT-Biodiesel process is based on hetrogeneous catalyst like Potassium carbonate, Barium sulfate, Calcium aluminate, Cobalt carbonate, Polyamine, Ammonical metal-oxide. Sodium, Potassium and Calcium Phosphates, mixture of metal oxides with alumina, Magnesium methoxide, Calcium oxide. Calcium ethoxide and Boron hydroxide, Calcinated hydro zeolite, and any other alkaline heterogeneous compounds available in market including the Anion ion exchange basic catalyst which can also be used like Amberlyst A-21, Amberlyst A26 or equivalent but not limited to, at a WHSV of 2 to 5. The operating conditions for transesterification are similar to esterification reaction.
The transesterification reactor effluent provides 100 percent conversion of triglycerides to Methyl Esters of the Fatty acid/triglycerides feeds. This is sent to gravity separator where glycerine settles at the bottom, as its specific gravity is 1.2 to 1.3. The methyl esters specific gravity is in the range of 0.85 to 0.9.
The biodiesel is taken from top of the separator and is washed with water before sending it to the storage. The glycerine is taken from the bottom of the gravity separator and is also washed with water before sending it to storage. Water wash will contain methanol that can be recovered by distillation and recycled to the process.